ARCHIVES

Features

October
2013, Vol.
25, No.10

Gritty information

Using
data for more-effective preliminary wastewater treatment

Joe Uglevich and Jimmie GriffithsAs
any wastewater treatment professional will attest, grit can wreak havoc at a
treatment facility. Yet rarely is the nature of grit quantified or understood
before upgrade projects or new system designs are undertaken. Most process
upgrades require extensive site-specific wastewater data (such as total
suspended solids and biochemical oxygen demand), but the first step in the
treatment train often is designed without taking these into account. Yet poor
grit removal, handling, and processing equipment selection and performance can
have significant effects on downstream unit processes. Read full article (login
required)

Bright lights, big city… smaller treatment systems?

Determining the cost and energy incentives of decentralized
treatment

Kartiki S. Naik and Michael K. Stenstrom

With
the increasing need for water reclamation, it is necessary to have a simple
system, not only to reclaim wastewater but also to convey it to the respective
area for reuse. Since reclaimed pipelines generally flow in the opposite
direction of sewers, they usually have to gain some elevation in their course.
Reducing the pipeline length is the principal solution used to minimize
pumping-energy consumption.

Centralized
water resource recovery facilities (WRRFs) generally cannot be located close to
all the potential reclaimed waste uses. It is especially difficult to establish
such a large WRRF in any residential neighborhood. Thus, for centralized WRRFs,
returning recycled water can require tremendous energy due to pumping. Adapting
the design of a large facility to local reclamation needs to reduce pumping
cost can be difficult.

But
what if one could optimize sewer networks and decentralized WRRF locations in
an urban area to minimize pump-back energy consumption for recycled water? One
research team computed pump-back energy consumption as a fraction of treatment
and aeration energy for a hypothetical but realistic example in the vicinity of
Hollywood, Calif. The team optimized the decentralized wastewater collection
and treatment configuration for Hollywood for minimum energy consumption and
cost. Read full article (login required)

What is the right
biomarker for water quality monitoring?

Pros
and cons of fecal coliforms, E. coli, and alternative microorganisms and how
they are used in watershed monitoring and water quality improvements

In
the late 19th century, researchers developed the total plate count method for
coliform colony counting as an indicator for pathogen and human health risk. By
the mid-20th century, technologies were developed to distinguish total
coliform, fecal coliform, and Escherichia
coli. In 1986, the U.S. Environmental Protection Agency (EPA) recommended
that E. coli be used as the indicator
organism for recreational waters. In 2012, EPA recommended that both E. coli and enterococci be used for
fresh waters.

In
the last few decades, advances in molecular tools have made it possible to
identify and quantify a large number of bacterial species without having to
culture them.

A
recent study undertaken by the Metropolitan Sewer District of Greater
Cincinnati and the University of Cincinnati used biological water quality data
— including fecal coliforms and E. coli along with some emerging pathogen
indicators (Bacteroides, E. coli
O157: H7, Norovirus, and Streptococcus) — to understand and
identify pollution in the Duck Creek watershed with molecular tools (Kapoor et
al., 2013). Read full article (login required)

What’s the best fit?

Waste
activated sludge (WAS) is characterized by low solids content, ranging from
0.25% to 2%, depending on operational condition. Prior to further stabilization
processes, WAS often is thickened to increase total solids concentration to
reduce the volume prior to anaerobic digestion, thereby decreasing the amount
of energy required to mix and heat the solids. Several technologies are
available for thickening WAS, such as gravity belt thickeners (GBTs),
rotary-drum thickeners, dissolved-air flotation, and decanter centrifuges.

Researchers
wanted to compare conventional and novel thickening technologies in economic
and environmental terms, carrying out the study in three steps. Read full article
(login required)

Operations Forum Features

Shaking the sand out

Grit-removal
design requires several considerations in facility retrofits and additions

Robert J. Kulchawik

Grit-removal
systems often are part of the first generation of unit processes at water
resource recovery facilities (WRRFs). Some of these facilities are still in
use, but many have gone through upgrades and are approaching 20 to 25 years in
age. Because of the abrasiveness of grit, the operations and maintenance costs
for these systems can be high.

However,
due to more-stringent effluent permit limits, many WRRFs are considering other
advanced treatment processes, such as biological nutrient removal, membrane
bioreactors, or other upgrades that can be adversely affected by the carryover
and accumulation of grit.

Thus,
there is a greater need for grit systems to achieve higher removal
efficiencies, either through retrofits or outright replacement. Retrofits and
additions often can face several challenges, including limited space for
construction of new processes, difficulty in maintaining existing grit removal
during construction, phasing of tie-ins, and hydraulic limitations. Read full article (login required)

Milford fights odor
and corrosion

Use
of pure oxygen improves sewer system safety and operation

Milford,
Conn., has an extensive sewer system that includes two water resource recovery
facilities, 42 pumping stations, and an extensive system of sanitary sewers. In
recent years, the system has been plagued with odor complaints and has
undergone severe corrosion problems caused by hydrogen sulfide.

Using
a combination of pump station modifications and the addition of a pure-oxygen
injection system the city has eliminated hydrogen sulfide production and thus
odor and corrosion problems. Read full article (login required)